I have a related question.
What is the point, other than adherence to rules, when a passenger turns up with a suitcase weighing 3 kilos over the allowance, of allowing them to transfer the 'offending' 3 kilos to hand baggage?
The overall load remains the same, but the extra weight (theoretically a few kilos per passenger multiplied by the number of passengers) of a tonne or so, is now in the overhead racks, meaning a higher CoG - not sure if that is relevant - and more space taken up, and more potential for injury if overhead lockers come open.